1. Field of the Invention
The present invention relates to a rechargeable battery using an inorganic solid electrolyte and a fabrication method thereof.
2. Related Art
As the quest grows for downsizing and weight-saving of electronic equipment, electrochemical storage battery cells also are more strongly demanded to satisfy such small-size/light-weight requirements. To achieve a battery which fully meets these requirements, ultra-small and ultra-thin batteries are under consideration, which are evolved from the integration or “collaboration” of thin-film architectures and battery material technologies. These thickness-reduced or “slim” batteries are expected to be used as power sources for integrated circuit (IC) cards and IC tags or to be mounted on large-scale integration (LSI) chip substrates.
On the other hand, high-power rechargeable batteries have been brought into practical use, including currently available lithium-ion rechargeable or secondary batteries having in combination a positive electrode made of lithium cobaltate, a negative electrode made of carbon material, and an electrolysis solution with lithium salts being dissolved in a nonaqueous solvent. While these are manufactured by various methods, one major approach for reduction to practice is to employ a process which includes the steps of depositing positive and negative electrode materials as slurried respectively, dehydrating resultant layers or membranes, cutting or “dicing” them into portions of a prespecified shape, rolling them under pressure, winding, and injecting thereinto an electrolysis solution. Unfortunately, such prior known methodology having these steps is encountered with limits to battery thinning and miniaturization.
Consequentially, in order to make batteries smaller and thinner, a low-profile solid-state electrolyte secondary battery has been proposed, which has its negative electrode made of metallic lithium or carbon, a positive electrode made of LiCoO2 or LiMn2O4, and an electrolyte element made of inorganic solid electrolyte material. The battery of this type is manufacturable by using semiconductor processes, such as sputtering, deposition or else, in combination with patterning techniques. Some of such battery are disclosed, for example, in Published Unexamined Japanese Patent Application Nos. JP-A-2000-106366 and 2004-127743.
As the prior known solid electrolyte batteries are fabricated by thin-film fabrication processes, such as sputter techniques, these batteries suffer from problems as to an increase in time consumed for film fabrication, difficulty in film lamination, and an increase in production costs. Another problem faced with the prior art solid electrolyte batteries is that since these are often designed to employ for the electrolyte certain metals such as copper, aluminum, gold, palladium or other similar high-conductivity metals, any intended thermal processing after film fabrication is incapable of being sufficiently performed. This is a serious bar to the achievement of excellent crystallinity of active material, resulting in the battery characteristics becoming deficient and inacceptable for practical use.